2026-08-16
If your NAS has been sluggish during rebuilds or write-heavy tasks, the culprit might not be your hardware — it could be the recording method your hard drives use.
As XDA explains in a solid breakdown, many drive manufacturers have quietly shifted consumer and even some "NAS-labelled" SKUs from Conventional Magnetic Recording (CMR) to Shingled Magnetic Recording (SMR). SMR overlaps data tracks like roof shingles to squeeze out more capacity per platter, but the trade-off is brutal: random writes tank, RAID rebuild times balloon, and ZFS/Unraid scrubs can crawl.
The worst part? Manufacturers haven't always been upfront about the switch. Seagate caught flak back in 2020 for shipping SMR Barracudas without clear labelling, and the situation hasn't improved much. WD desktop drives, Toshiba P300s — plenty of common picks are SMR underneath.
Why homelabbers should care
- RAID rebuilds on SMR can take days instead of hours, leaving your array vulnerable to a second failure.
- ZFS resilver and scrub performance drops significantly, especially on pools with high utilisation.
- Write caching masks the problem initially — SMR drives seem fine until the cache fills, then performance falls off a cliff.
What to look for
Stick with confirmed CMR drives for any NAS or server duty. The usual safe bets: Seagate Ironwolf or WD Red Plus (not the standard WD Red, which has been SMR in smaller capacities). Toshiba N300s are CMR too and often cheaper per TB in the UK.
Generally, drives 8TB and above are almost always CMR due to platter physics, but always check the manufacturer's spec sheet before buying — don't rely on the box marketing.
Honest caveat
SMR drives are perfectly fine for cold storage, backups, or single-drive setups where sequential writes dominate. They're not evil — they're just wrong for multi-drive NAS arrays.
If you're pulling drives to test or clone before committing to a NAS, a M.2 SSD Enclosure – NVMe & SATA USB External Aluminium Case is handy for quickly checking SMART data on spare SSDs too.
Bottom line: check your drives, check the spec sheets, and don't assume "NAS" on the label means CMR inside.